EXOPHTHALMOMETRY

• Abnormal protrusion of one or both eyes is called proptosis (or exophthalmos). Proptosis is caused by an increased mass in the orbit behind the globe. Because the bony orbit is rigid, any increase in the volume of its contents will push the globe forward.

• The Hertel exophthalmometer is a handheld instrument that uses mirrors to help the examiner visualize the eye from the side and measure the position of the corneal apex with respect to the lateral orbital rim.

• The globe is usually positioned at the front of the orbit so that in primary gaze, the anterior point of the cornea is 12 to 20 mm in front of the plane of the orbital opening. The average distance between the lateral orbit rim and the corneal apex is 16 to 18 mm; there should be no more than 1 to 2 mm difference between the measurements of the 2 eyes.

What the Patient Needs to Know

• This test is to measure any protrusion of your eye(s).

• You should be seated comfortably and remove your glasses.

• The instrument will be placed against your outer eye sockets and may be slightly uncomfortable, but not painful.

• Keep both eyes open and look straight ahead while the examiner moves from sideto side.